Slew rate control circuits for IO pads have been used to limit RLC oscillation of signals being driven off-chip and to limit simultaneously switching output (SSO) noise. However, conventional slew rate control circuits have a disadvantage of increasing propagation delay through an IO pad. Most IO pad designers are familiar with a trade off between slew rate control and propagation delay.
Slew rate control circuits are used in IO buffers of computer adapter cards. An adapter card designed for a PCI bus would have a particular propagation delay and slew rate control to meet the standard PCI specification. However, a PCIX bus specification (e.g., an enhanced version of the PCI bus) has a much more forgiving slew rate control requirement and much tighter propagation delay requirement than the standard PCI specification. An adapter card designed for use with the PCIX bus would need to provide less slew rate control, but much faster propagation delay. Since the PCIX bus is an enhanced version of the PCI bus, an adapter card that could operate on both buses would provide an advantage of easy migration from the PCI bus to the PCIX bus.
Conventional control circuits select between different propagation delays or different slew rates. However, the conventional circuits do not simultaneously select between different propagation delays and different slew rates.
A solution to select between different propagation delays and different slew rates simultaneously would be desirable.